Means for translating vibrations



Patented Mar. 3, 1925.

UNITED STATES PATENT OFFICE.

WALTER. EAHNEMANN, OF KITZEBERG, NEAR KIEL, AND HEINRICH HECHT ANDBERNEABD SETTEGAST, 0F KIEL, GERMANY, ASSIGNORS '10 SIGNAL GESELL-SGHAJET MIT BESCHRANKTER KAFTUNG, OF KIEL, GERMANY.

MEANS FOR TRANSLATING VIBRATIONS.

Application filed November 4,1921. Serial No. 512,946.

To all whom it may concern:

Be it known that we, WALTER HAHNE- MANN, HEINRICH HECHT, and BERNHARDSET'IEGAST, citizens of the German Republic, and residing at Kitzeberg,near Kiel, and at Kiel, county of Schleswig-Holstein, State of Prussia,Germany, have invented .certain new and useful Im rovements in Meansfor- Translating V1 rations (for which we have filed applications forpatent in Germany on September 25th, 1920; 00-

tober 2nd, 1920; October 28th, 1920; March 7th, 1921; and September24th, 1921; and in Ar entina on July 12th, 1921), of which the fo owingis a specification.

One of the most important problems that has to be faced particularlyfrequently by engineers dealing with mechanical vibrations is totransfer vibrations with the smallest possible loss of energy from onevibratory body or unit to another vibratory body or unit. When the ratioof force to motion of one of the vibratory bodies or units is differentfrom the ratio of force to motion of the other vibratory body or unit,the problem of transmission or transfer of sound from one to the othereffectively and efficiently becomes more difficult. One form oftransferring or transmitting means is disclosed in a copending applicaton, Serial No. 435,563, filed January 6, 1921. The present applicationis directed to another form, which is adapted for use in some caseswhere the former is not well suited.

The transferring or transmitting means according to the presentinvention is a s ace oscillation system, which comprises a ual chamber,the individual compartments of which are in communication with eachother by a passage or passages, the dual chamber being designed so thatit has only one fundamental oscillation, in other words so that thesystem is a one wave system. By analogy to the copending application,Scr. No. 435,563, in the resent case the elastic forces reside in theuid in the individual chambers or compartments while the mass of thesystem is represented by the fluid vibrating through the communicatingpassage or passages.

' As has already been stated, a particular object of the presentinvention is to solve the problem of efficiently transferring soundvibrations from one vibratory body to another where these vibratorybodies have different amplitude-to-force ratios. To this end the dualchamber is especially designed. The solution of the problem consists inproviding a dual chamber in which in each individual compartment theamplitude-toforce ratio of the sound vibrations is made to reach orapproximately reach or corres' ond to the amplitude-to-force ratio ofthe vibratory body next to it. This amplitudeto-force ratio in eachcompartment is determined by the size of the compartment. Furthermore,by suitably dimensioning each compartment the damping eflect thereofmaybe made to reach a desired magnitude. The required size of eachcompartment may be determined either by experiment or calculation orboth.

Other and further features of the invention will be describedhereinafter in the specification and be more particularly pointed out inthe annexed claims.

The invention will now be described, by way of example, with referenceto the accompanying drawing, in which like reference letters andnumerals in the several figures designate like parts.

Fig. 1 is a section of a dual chamber I formed of two individualchambers or compartments that communicate with each other through acentral passage.

Fi 2 represents a section of a dual cham er with a plurality ofcommunicating passages in its dlviding wall Fig. 3 is a section of adual chamber such as shown in Figure 2, but in which one of theindividual compartments is next to a vibratory diaphragm while the otheris next to a sound conducting tube or conduit.

Fig. 4 is a section of a dual chamber applied to a megaphone, in whichone of the individual compartments is next to a vibratory diaphragmwhile the other flares out into the open air.

Fig. 5 is a section of a dual chamber s stem formed of two dual chamberscoup ed together in series, the central compartment of the system inthis case being common to the two dual chambers.

In Figure 1, c and e, designate the i11d1-- vidual compartments of adual chamber constructed in accordance with the invention, and 0designates the communicating or connecting passage between the twocompartments. Z is a sound conducting conduit or pipe, and Z is asimilar pipe of larger diameter connected to the former by the vibratoryunit that the dual chamber constitutes. The purpose of the dual chamberin the arrangement shown in this figure is to transfer sound from thesmall conduit or pipe Z, to the larger conduit or pipe Z, The Walls ofthe chamber e are preferably shaped, as shown, so as to converge towardthe sound passage 0, in order that as little resistance as possible isoifered to the oscillations and that the oscillations will beconcentrated toward the sound passage 0. Since the conduit Z is ,ofsmaller sectional area than the conduit Z it will be observed that thecompartment e, is of smaller volume than the compartment e,.

In the dual chamber shown in Fig. 2, instead of one communicatingpassage 0 there are a plurality of such passages distributed over arelatively large area of the partition wall. In this type of dualchamber it is not absolutely necessary to converge the walls of theindividual compartments toward the communicating passages as in Figure1, although this may be done if desired. By distributing thecommunicating passages over the partition wall the advantages are as'ingained that the total distances traversed by the oscillating medium arereduced and this medium is prevented from passing straight through thecompartments. In this figure,

igure 1, the conduit Z is smaller than the conduit 1 and, therefore, inaccordance with the invention, the compartment e must be, as shown,smaller than (2,.

The embodiment of the invention shown. in Figure 3 is the same as thatshown in Figure 2, except that the com artment e, is closed off by adiaphragm instead of being in communication with a conduit -or pipe L,.This diaphragm d carries. or forms the armature a of an electromagnet m.Because of the mass and elastic force of the diaphragm d it is necessaryto make the compartment e, quite small.

As a rule the size given to each of the two individual compartments willpreferably be short with reference to the wavelength of the soundtransferred, so that the waves that occur in them are quasi stationary,i. e., that the motions of all parts of the medium in each compartmentare substantially in phase with each other.

In regard to the dimensions of the dual chamber, a point to beinvariably observed is that the-external surface area of the circularwall of animaginary cylinder whose length and cross-sectional areacorrespond to the depth of either compartment of :the dual chamber andto the cross-sectional'area of the communicatin passage respectively,must be at least as Iarge as the cross-sectional area of the saidcommunicating passage itself; and, in addition, the C1'088-SBO- tionalarea of the sound passage must not be greater than the cross-sectionalarea of either compartment at any point taken on a plane parallel to thecross-sectional plane of the sound passage, because if this is not sothe greatest motion of the sound conducting medium will not take placeas it should in the said sound passage, but at the point of smallercross-section.

In Fig. 4 a form of the invention is shown in which the one compartmente is arranged to contain a quasi-stationary wave, while the medium inthe other compartment e is not in a strict sense quasistationary. Thecompartment e is here formed by the flaring trumpet or megaphone piece25. A condition, somewhat analogous to a quasi-stationary condition, maybe said to be produced in the compartment 6 due to the inertia of theoutside medium. The complete apparatus of Fig. 4 constitutes an improvedmegaphone, the voice being directed into the mouthpiece it against thediaphragm d, which latter excites the dual chamber e,, e whose trumpetshaped compartment e then throws the sound into the air.

Fig. 5 shows a dual chamber system formed of two dual chambers coupledtogether, one of these dual chambers bein composed of compartmentse andc an connectin chamber icing composed of compartments (2, and 6 andconnecting passage 0. In this arrangement, it will be observed, thecompartment e is common to the two dual chambers, in the same Way as inthe device disclosed in copending application, Serial No. 435,563,previously referred to, a mass may be common to two coupled v.bratorystructures. Where the common compartment e, is relatively large, asshown, a loose coupling between the dual chambersjs secured. Of course,more than two dual .chambers could be coupled together.

A certain portion of the total amount of vibratory energy operating inthe entire dual chamber arises in each of the two compartments a, and0,, and the quota of energy in each is determined by the relative sizesof the compartments. The energy in each of the compartments is in theform of pressure energy, while taking the form of motional or kineticenergy in the communicating passage or passages. The ratio of themagnitudes of the pressure amplitudes in passage 0, and the other dualcompartments whose size is 6 and e, is determined by the ratio of thesesizes, the smaller compartment having the higher pressure and the largercompartment the lower pressure.

To make sound communication apparatus efiicient, attention must be givento certain special requirements concerning the damping thereof.

It is known to be desirable in sound receiving apparatus to have theso-called useful damplng of the apparatus (due to actuating theapparatus) equal to the so-called radiation damping of the apparatus(due to the reflection or radiation of energy back into the soundpropagating medium). On the other hand, in sound sending apparatus it isknown to be desirable to have the radiation damping of the highestpossible magnitude. In acoustic apparatus heretofore, however, theseconditions have not been satisfied. But with the invention of thepresent dual chamber or two-compartment resonator, a convenient means isprovided whereby, by the suitable dimensioning of the individualcompartments, the radiation and useful dampings may be regulated oradjusted to meet desired conditions or magnitudes. The required sizes ofthe individual compartments in each case to effect certain dampingconditions may be determined either by experiment or calculation.

If the air in the dual chamber is the only vibratory element or body inthe entire apparatus that is to have a pronounced natural rate ofvibration, then this chamber itself,

and this chamber only, must be tuned to the frequency of the sound to bereceived or sent out.

Considerations on the physical properties of a dual chamber lead to thefollowing:

From the analo between the invention disclosed in copen ing application,Ser. No. 435,563, and the dual chamber, which was pointed out in theopening paragraphs, it follows that in the first place the dual chamberis'a monotone (single wave) structure. As in the structure disclosed insaid copending application, the vibratory energy sometimes resides inthe two masses or weights in the form of kinetic energy, and at othertimes in the stretched or compressed connecting rod between the twomasses in the form of potential energy, so in the dual chamber itresides sometimes in the two compart- This also holds in cases in whichthe elastic element gas in the chambercoop ments in the form ofpotential energy (causing increased pressure in one compartment anddecreased pressure in the other) and at other times in the form ofkinetic energy in the flowing medium in the communicating passage. Thisstatement also holds in cases in which the vibrating medium in one orboth of the compartments of the dual chamher is not quasi stationary,and even when these compartments individually act as resonators,although in such a case the resonance eifect produced independently byone or both compartments would affect the natural rate of vibration ofthe dual chamber to a very great extent.

Another fact that may be drawn from comparison with the device ofcopending application, Ser. No. 435,563, is that when a series of dualchambers are coupled together as in Figure 5, a bi-resonant ormulti-resonant system is produced which in regard to tuning and dampingis subject to the laws applying to coupled vibratory systems.

Formulas have been found by means of which the sizes of the compartmentsof a dual chamber can be determined in accordance with the invention ineach, particular case. This will now be elucidated by a fewexamples:

If E denotes the amount of vibratory energy operating in the'onecompartment 0,, and E the vibratory energy in the other compartment 6then, according to the law stated above,

Let it be assumed that the problem to be dealt with is to continuallytransmit or transfer sound energy from one tube Z, (of larger diameter)to another tube Z, (of small diameter). In Fig. 1, for example, thiswould be in the direction from right to left. In such a case thecompartments c and e are made of such sizes that the damping of the duelchamber e -e due to l, is equal to the damping caused by Since the tube3,, of lar er diameter produces the greater damping eflect, thevibratory energy operating in e must be made proportionately smaller, i.e., the compartment emust be made proportionately larger than 6 or inother words so much larger that the. damping of the dual chamber that isto be attributed to Z is equal to the damping produced by Z If for somereason, as in order to obtain a resonance curve of a certain breadth,the said individual damping is to have a certain pre-- are as follows:According to a known law the damping d is always equal to one half ofthe ratio of the amount of energy (E yielded per second by a vibratorystructure to the total amount of energy E operating in the structure, i.e.,

1 E an e g2dE.

Another example will now be explained with reference to Fig. 3 of thedrawing. Suppose that the diaphragm cl is excited by the electromagnetm, and that sound en ergy is to be conducted out of the dual chamberthrough the tube L The first problem to be faced here is tocause such anamount of the particular form of vibrations produced in the diaphragm bythe exciting magnet to pass into the air compartment c as is given bythe desired damping of the sender. This is accomplished by selecting theproper relation between the size of this compartment (small couplingchamber) and the diaphragm. Then it is necessary to conduct into thetube an amount of the said vibratory energy which is given by thedesired damping. This functionis performed by the compartment e In thisinstancewe have to deal with two vibratory bodies or units, one of whichconsists of the diaphragm and the compartment 6 while the other consistsof the dual chamber 6 6 The two are coupled together by 6 Therefore, ata given coupling, there should be a certain relationship between thesize of the compartment e and the elastic force of the diaphragm on theone hand, and between the sizes of e, and e, on the other hand. Thedamping of the vibratory system should be produced at e, by the tube,the form of damping meant here being the useful damping due to thepropagation of sound energy through the tube.

Dual chambers as contemplated herein are of particular importance in theconstruction of submarine sound receivers in which a diaphragm abuttingon the water transfers the sound energy it receives to the other partsof the apparatus through a small chamber bounded by the diaphragm. Thepractice adopted heretofore has been to cause the said small chamber toact directly, or indirectly through a resonator, upon thesound-conducting tube, and no particular points were observed regardingthe specific properties of the resonator used. In ac cordance with thisinvention it is preferable to interpose between the diaphragm and thetube a dual chamber comprising air compartments of such a kind that thesound waves operating in them are quasi stationary, the size of thecompartment next to the diaphragm being selected with due.

consideration to the desired coupling between the dual chamber and thediaphragm, and the ratio of the compartment next to the diaphragm to thecompartment next to ratus of any kind and for any purpose, so

as to enable sound energy to be transmitted or transferred at thegreatest possible efliciency.

The term vibratory body is used in the claims in its broadest sense,including for example a vibratory body or columnof gas; and the wordpassage used therein is intended to designate not only a passage formedby a single aperture as in Fig. 1, but also a passage formed of aplurality of apertures as in Fig. 2.

We claim 1. A resonator formed of two individual compartments connectedby a sound passage, and having each compartment of predetermined sizedependent upon the amplitudeto-force ratio of the vibratory body next tothe particular compartment.

2. A resonator formed of two individual compartments connected by asound passage, and having each compartment of predetermined sizedependent upon the damping effect to be produced in the particularcompartment.

3. A resonator formed of two individual compartments connected by asound passage, and having each compartment of predetermined sizedependent upon the amplitude to-force ratio of the vibratory body nextto the particular compartment, the cross-sectional area of said passagebeing not greater than the smallest cross-sectional area of eithercompartment taken on a parallel plane, and the external surface area ofthe circular wall of an imaginary cylinder having the samecross-sectional area as'the passage and having a length equal to thelength of either compartment being at least as large as thecross-sectional area of said passage.

4. Means for transferring sound between two vibratory bodies, comprisinga dual chamber formed of two individual compartments connected by asound passage and tuned as a whole to the frequency to be transferred,and having each compartment of predetermined size dependent upon theamplitude-to-force ratio of the vibratory body next to the particularcompartment.

Means for transferring sound between two vibratory bodies, comprising adual chamber formed of two individual compartments connected by a soundpassage and tuned as a whole to the frequency to be transferred, andhaving each compartment of predetermined size dependent upon the dampingefiect to be produced in the par ticular compartment.

6. Means for transferring sound between a conduit of relatively smallcross-section and a conduit of relatively large cross-section,comprising a dual chamber formed of two individual compartmentsconnected by a sound passage, and having each compartment ofpredetermined size dependent upon the amplitude-to-force ratio of thevibratory body next to the particular compartment, the compartment nextto the conduit ofv relatively small cross-section being the smallercompartment.

7. Means for transferring sound between a conduit of relatively smallcross-section and a conduit of relatively large cross-section,comprising a dual chamber formed of two individual compartmentsconnected by a sound passage, and having each compartment ofpredetermined size dependent upon the damping effect to be produced inthe particular compartment, the compartment next to the conduit ofrelatively small crosssection being the smaller compartment.

In testimony whereof we aflix our signatures.

WALTER HAHNEMANN. HEINRICH HEOHT. BERNHARD SETTEGAST.

